Spatio-temporal running parameters and their variability help to determine a runner's running style. However, determining whether a change is due to the measurement or to a specific condition such as an injury is a matter of debate, as no recommendation on the number of steps required to obtain reliable assessments exists. What is the optimal number of steps required to measure different spatio-temporal parameters and study their variability at different running speeds? Twenty-five runners performed three experimental sessions of three bouts of treadmill running at 8, 10 and 12 km/h separated by 24 h. We measured cadence, stride, step, contact and flight time. We calculated the duty factor and the leg stiffness index (Kleg). Mean spatio-temporal parameters and linear (coefficient of variation, standard deviation) and non-linear (Higuchi fractal index, α1 coefficient of detrended fluctuation analysis) analyses were computed for different numbers of steps. Relative reliability was determined using the intraclass coefficient correlation. The minimal number of steps which present a good reliability level was considered as the optimal number of steps for measurement. Absolute reliability was assessed by calculating minimal detectable change. To assess the mean values of spatio-temporal running parameters, between 16 and 150 steps were required. We were unable to obtain an optimal number of steps for cadence, stride and step-time variabilities for all speeds. For the linear analyses, we deduced the optimal number of steps for Kleg and the contact time (around 350 steps). Non-linear analyses measurements required between 350 and 540 steps, depending on the parameter. Researchers and clinicians should optimize experimental conditions (number of steps and running speed) depending on the parameter or the variability analysis targeted. Future studies must use absolute reliability metrics to report changes in response to a specific condition with no bias due to measurement error.

中文翻译：

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评估获得可靠运行时空参数及其变异性的最佳步数

时空跑步参数及其变异性有助于确定跑步者的跑步风格。然而，确定变化是由于测量结果还是由于特定情况（例如受伤）引起的仍然存在争议，因为没有关于获得可靠评估所需步骤数量的建议。测量不同时空参数并研究它们在不同运行速度下的变化所需的最佳步数是多少？ 25 名跑步者以 8、10 和 12 公里/小时的速度在跑步机上进行了 3 次实验，每次跑步间隔 24 小时。我们测量了步频、步幅、步数、接触时间和飞行时间。我们计算了占空因数和腿部刚度指数 (Kleg)。计算不同步数的平均时空参数以及线性（变异系数、标准差）和非线性（Higuchi 分形指数、去趋势波动分析的 α1 系数）分析。使用组内系数相关性确定相对可靠性。表现出良好可靠性水平的最小步骤数被认为是测量的最佳步骤数。通过计算最小可检测变化来评估绝对可靠性。为了评估时空运行参数的平均值，需要 16 到 150 步。我们无法获得所有速度的步频、步幅和步速变化的最佳步数。对于线性分析，我们推导出 Kleg 的最佳步数和接触时间（大约 350 步）。非线性分析测量需要 350 到 540 步，具体取决于参数。研究人员和临床医生应根据参数或目标变异性分析来优化实验条件（步数和运行速度）。未来的研究必须使用绝对可靠性指标来报告针对特定条件的变化，而不会因测量误差而产生偏差。